Mechanism for gradually and smoothly varying rotational speed between a drive member and a driven member

ABSTRACT

A mechanism for varying rotational speed between two rotary shafts, namely a drive shaft and a driven shaft. The mechanism is designed to replace gear boxes which are generally used in motor vehicles. The mechanism includes two truncated cones with concave surface generatrices attached to a shaft secured to the engine and to a shaft secured to the transmission members, respectively. A roller made up of an inverted double cone having convex surface generatrices is mounted on an arm via a pin and arranged to rotationally interconnect the truncated cones by means of the adherence caused both by the choice of materials and by the bearing force exerted on the truncated cones by the roller through a suitable pressure member. The roller is translationally movable over the convex surfaces of the truncated cones by means of a suitable position varying system for adapting the drive ratio to the various parameters which influence the operation of the whole mechanism, according to its position. The mechanism is particularly suitable for use in motor vehicles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mechanism for gradually and smoothlyvarying the rotational speed between a driving member and a drivenmember.

2. Description of the Related Art

It is sometimes necessary not to interconnect the driving shaft directlyto the movement transmission members. This is all the more true whenthere is an internal combustion engine which cannot be started whenengaged since it provides an appreciable torque only from a certainrotational speed.

The maximum driving torque available from a given engine isapproximately constant, while the resistance to be overcome to ensuremovement can vary continuously. In a motor-car, the propelling powermust be equal to the repelling power so that it can move at a determinedspeed. The repelling torque varying continuously with the profile of theroad, it would be desirable that the drive ratio between the rotationalspeeds of the engine and of the propeller shaft be responsive to theprofile fluctuations, which amounts to having continuous gear shifting.

To vary the drive ratio, the following are generally used : gear boxeshaving various compound trains which can be activated at will, gearboxeshaving epicycloidal trains, torque converters as well as driving beltpropeller means.

The use of these systems requires one to frequently modify the driveratio according to the changes of the repelling power, which causes theengine speed to be varied and entails a specific consumption moresignificant than with a constant speed.

The mechanism according to the invention allows to overcome suchdrawbacks by enabling the speed changes in a continuous and progressiveway, while enabling the engine to run at a constant speed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents the mechanism according to a preferred embodiment thepresent invention.

FIG. 2 shows the speed-varying mechanism according to a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The mechanism represented in FIG. 1 comprises a truncated cone (3)attached to a shaft (2) rotationally driven by a driving member (1), anda truncated cone (5) mounted on a shaft (6) attached to the movementtransmission members. The truncated cones (3, 5), the generatrices ofwhich form concave conic frustums, are mounted in an oppositeconfiguration so that the narrow end of one can correspond to the wideend of the other one. The transmission of the rotational movement fromthe truncated cone (3) to the truncated cone (5) is effected by a roller(4). Roller (4) is composed of two inverted truncated cones sharing thesame axle (a), the generatrices of which form convex conic frustums.

Adhesion of roller (4) on truncated cones (3, 5) is ensured by the forcetransmitted by a pressure member (7). Roller (4) can move laterally bymeans of a varying system (8) enabling it to slide the length oftruncated cones (3, 5).

At the beginning of the start-up phase, roller (4) has one of itsfrustums in contact with the smallest diameter of the driving truncatedcone (3) while the other one is in contact with the largest diameter ofthe driven truncated cone (5); such a configuration corresponds with thelowest ratio. Pressure member (7) must provide a pressure forcesufficient to obtain an adhesion between roller (4) and truncated cones(3, 5) that is at least equal to the driving torque.

The adhesion is enhanced by use of materials having a high frictioncoefficient on the surface of truncated cones (3, 5) and roller (4).

The use of truncated cones requires converging vertices for eachposition of roller (4). This is achieved by giving the frustums of eachtruncated cones (3, 5) and roller (4) a particular radius of curvature.

The use of concave or convex shapes enables the vertex of truncatedcones (3, 5) to be moved along their respective axles while achieving aperfect convergence of the vertices for each position occupied by roller(4).

When it is desired to increase the rotational speed of the driven shaft(6), it is sufficient to vary the roller position (4) by having it slidealong truncated cones (3, 5) by means of a varying system (8). The driveratio is gradually varying to pass from the lowest ratio to the highestratio and vice versa by tilting roller 4 around its vertical axis, asshown in FIG. 2.

This system allows continuous gear changing without requiring thechanges in the engine speed which can be used in the range of maximumtorque. It then becomes worthwhile to use an engine having an importanttorque for a low specific consumption. This configuration allows rapidaccelerations and high speeds which can be compared to those of morepowerful propelling systems, all the while keeping the engine speedwithin a range of use favoring low consumption. Accordingly, thelongevity of the engine is greatly increased.

Similarly, the controlled variation of the drive ratio by any systemallows for a powerful engine braking as soon as the accelerator pedal isreleased, which increases the longevity and the efficiency of the brakesystem. This system enables significant safety improvements.

The mechanism according to the invention is particularly adapted for themotor vehicles.

I claim:
 1. A mechanism for a continuous variation of the rotationalspeed between a driving member and a driven member comprising;a drivingmember; a rotatable driving shaft mounted to the driving member andhaving an axial direction; a driving cone engaging and axially alignedwith the driving shaft, the driving cone being truncated and having asurface with a concave generatrix and a tapering direction; transmissionmembers; a rotatable transmission shaft mounted to the transmissionmembers and having an axial direction, the axial direction of the secondshaft being divergent from the axial direction of the first shaft; atransmission cone engaging and axially aligned with the transmissionshaft, the transmission cone having a surface with a concave generatrixand a tapering direction substantially opposite to the taperingdirection of the driving cone; and a roller engaging the driving coneand the transmission cone and having an axis and an outer surface with adriving side and a transmission side, each of the two sides being in theshape of a truncated cone, the two cones being joined at the bases ofthe codes and having convex surface generatrices the driving side andthe transmission side of the roller being in contact with the drivingcone and the transmission cone, respectively.
 2. The mechanism accordingto claim 1, further comprising a pressure member for preventing any lossof adhesion between the roller surfaces and the driving cone and thetransmission cone.
 3. The mechanism according to claim 1, whereinvariation of a roller position along the driving and transmission conesis obtained by the roller turning in one direction or the other around avertical axis of the roller, the turned roller having a screwingmovement on the driving and transmission cones to therefore enable theroller to be moved along the generatrices of the driving andtransmission cones whereby an increase or decrease in a drive ratio isobtained according to the variation of the roller position.
 4. Themechanism according to claim 2, wherein variation of a roller positionalong the axial directions of the driving and transmission cones isobtained by the roller turning around a vertical axis of the roller forthe roller to have a screwing movement on the truncated cones totherefore enable the roller to be moved along the generatrices of thedriving and transmission cones whereby an increase or decrease in adrive ratio is obtained according to the variation in the rollerposition.
 5. The mechanism according to claim 1, further comprisingmeans for translationally moving the roller along the surface of eachtruncated cone.
 6. The mechanism according to claim 5, wherein each ofthe convex cone-shaped sides of the roller, the driving cone and thetransmission cone has a vertex, the vertices of the sides of the rollerconverging with a respective one of the driver and transmission conevertices in any position of the roller along the driver and transmissioncone surfaces on which the roller is translationally moved.
 7. Themechanism according to claim 1, wherein the roller axis defines an upperroller half and a lower roller half, and the roller sides on the lowerroller half contact the driver and transmission cones.
 8. A variablespeed mechanism, comprising:a drive shaft with a conical outer surfacehaving a concave generatrix and being rotatable about a drive axis; atransmission shaft with a conical outer surface having a concavegeneratrix and being rotatable about a transmission axis; and a rollerhaving an axis and an outer surface in contact with the outer surface ofthe driving shaft and the outer surface of the transmission shaft fortransmitting power between the driving shaft and the transmission shaft,the outer surface of the roller including two conical roller surfaces,each of the two conical roller surfaces having a convex generatrix. 9.The variable speed mechanism of claim 8, further comprising means forpressing the roller into contact with the outer surface of the drivingshaft and the outer surface of the transmission shaft.
 10. The variablespeed mechanism of claim 8, further comprising means for changing analignment of the axis of the roller with respect to the axes of thedriving shaft and the transmission shaft for translationally moving theroller along the outer surfaces of the shafts.
 11. The variable speedmechanism of claim 10, wherein each of the two conical roller surfacesand the outer surfaces of the shaft has a vertex, and projections of thevertices of the two conical roller surfaces converge with projections ofthe vertices of the respective outer surface of the shafts at anyposition of the roller when moved translationally along the outersurfaces of the shafts.